The field of the invention is ventilation systems for use with institutional and commercial cooking equipment.
Kitchen hoods can be categorized into two types, compensating and non-compensating. The non-compensating hood includes an exhaust system which draws contaminated air from above the cooking equipment and carries it through ductwork to the outside. Make-up air is supplied to the kitchen from a separate source such as the building's heating or cooling plant. A compensating hood, on the other hand, has an integral air supply system which introduces the proper amount of make-up air into the kitchen. Although compensating hoods are more complex, and hence more expensive, the make-up air can be carefully controlled on such hoods to insure proper operation of the ventilation system.
Of course the primary objective of kitchen hood design is to effectively exhaust contaminants generated by the cooking equipment. An objective of ever-increasing importance in recent years is the efficiency with which the hood performs this function. In each of these designs (compensating or non-compensating) make-up air must be introduced into the kitchen to replace that being exhausted, and at extreme outside temperatures, this make-up air must be heated or cooled to acceptable levels. The heating or cooling of this make-up air is becoming more expensive due to the rapidly escalating energy costs.
There are numerous guidelines and codes which apply to the design of kitchen ventilation systems, and in most installations these codes require that a specified minimum amount of air be exhausted. This specified amount may be determined by the type and size of cooking equipment beneath the hood or by the area which the hood covers. In all cases the amounts specified are intended to deal with worst case situations which seldom occur in practice. As a result, the ventilation system is required to exhaust and to supply make-up air in quantities far in excess of that actually needed to exhaust contaminants and odors. In addition, these specified amounts of air must be maintained even though not all of the cooking equipment beneath the hood is in operation.
Efficiency of kitchen ventilation systems can be increased greatly by entering fresh outside air as part or all of the make-up air. As disclosed in U.S. Pat. No. 4,134,394 for example, make-up air is supplied from one source which provides fresh air from outside the building and a second source which provides conditioned, or "tempered" air. The outside fresh make-up air is not directed into the kitchen area, but is instead directed beneath the hood. This practice maintains the amount of exhaust air required by applicable codes and reduces the tempered air removed from the kitchen. Since the tempered make-up air may only comprise a percentage of the total make-up air (depending upon the cooking equipment beneath the hood), a considerable energy savings is achieved over non-compensating hoods which require one hundred percent tempered or conditioned make-up air.
Although prior overhead canopy kitchen hoods provide means for reducing the amount of tempered make-up air while maintaining the total amounts of exhaust air required by applicable codes, none provides means for further reducing the amount of tempered make-up air when less than all of the cooking equipment is in operation. In an installation containing an oven, fryer, range and charbroiler, for example, the following amounts of exhaust air may be needed for adequate ventilation:
Oven--375 cubic feet/minute PA1 Fryer--255 cubic feet/minute PA1 Charbroiler--1133 cubic feet/minute PA1 Range--496 cubic feet/minute
The kitchen hood is sized and the ratio of fresh make-up air to tempered make-up air is set to handle the total ventilation load, which in this example is 2259 cubic feet of tempered air per minute. If the user operates only the oven, as is typical in institutions which do their own baking, a total of 1884 cubic feet per minute of tempered air is exhausted unnecessarily. Indeed, considerable energy is wasted through the exhaust system when all but the charbroiler are operational and in many installations the charbroiler may only be operated for short periods of time just prior to meals. In other words, prior kitchen ventilation systems waste considerable amounts of costly energy when all of the cooking equipment is not in operation.